Inkjet systems have been used in many printers because the system can be configured with a compact and inexpensive device and because images can be formed on recording media in a non-contact manner. In inkjet systems, ink is ejected from an ink-ejecting opening such as a nozzle. Among inkjet systems, piezo-inkjet systems and thermal-inkjet systems enable high resolution and high speed printing. The piezo-inkjet systems utilize deformation of piezoelectric elements to eject ink and the thermal-inkjet systems utilize boiling of ink caused by application of thermal energy to eject ink.
Currently, it has become important to increase the processing speed and improve the image quality during printing on plain paper or non-water-absorbing recording media such as plastics by inkjet printers. In particular, prolonged drying time for droplets after printing causes practical problems such as a tendency for image bleeding to occur. And not only does interference between ejected droplets due to intermixing between adjacently ejected ink droplets occur, thereby inhibiting formation of sharp images, it is also necessary to dry the printed media without stacking immediately after printing because the solvent drying speed is extremely low when non-water-absorbing recording media are used. The interference between ejected droplets is a phenomenon wherein adjacently ejected droplets fuse with each other in order to reduce surface energy (reduce surface area). When the adjacent droplets fuse with each other, the positions of the droplets are shifted from the initial ejected positions, causing unevenness of line width especially when thin lines are drawn with colorant-containing ink and unevenness appears when a surface is drawn.
For prevention of image bleeding and interference between ejected droplets, an inkjet ink that is cured and fixed not by vaporization of its ink solvent but by radiation is proposed as a method of accelerating ink curing (e.g., JP-A No. 5-214279). The ink often has a problem of insufficient storage stability, because undesirable polymerization reactions often occur easily during storage due to coexistence of polymerizable compounds and polymerization initiators.
Methods of using a two-liquid type ink and allowing the two liquids to react on a recording medium are proposed for improvement in both storage stability and drying speed. Examples of such methods include a method of applying a liquid containing a basic polymer and then an ink containing an anionic dye (e.g., JP-A No. 63-60783), a method of applying a liquid composition containing a cationic substance and then an ink containing an anionic compound and a colorant (e.g., JP-A No. 8-174997), and a recording method of using two inks, one containing a photo-curing resin and the other containing a photopolymerization initiator (e.g., Japanese Patent No. 3478495).
However, these methods, which are aimed at suppressing image bleeding by precipitation of the dye itself, are not effective in suppressing interference between ejected droplets and lowering drying speed because of using an aqueous solvent. Also there are concerns about deterioration in image quality because the precipitated dye is easily distributed unevenly on the recording medium.